Higher primary alcohols, such as those in the C10-C18 range, are well known and useful compounds which are suitable for a wide variety of products and applications. For example, they can be usefully converted to surfactants by sulphation and/or ethoxylation and used in laundry detergents and other household cleaning products.
Methods for producing primary alcohols are well known in the art. Unfortunately, it is not commercially viable to produce primary alcohols directly from the oxidation of paraffins. This is because the oxidation of paraffins produces primarily secondary alcohols, tertiary alcohols or ketones, or a mixture of these compounds, but does not produce high yields of primary alcohols. Therefore, despite paraffins being a relatively inexpensive feedstock, it is necessary to use other methods of producing primary alcohols.
One well known and commercially used method for producing primary alcohols is the hydroformylation of olefins using a homogeneous hydroformylation catalyst. Using such a method, primary alcohols of high selectivity and yield can be produced. For such methods it is necessary to use an olefin feed as starting material. Olefins can be produced by various methods including the oligomerisation of ethylene.
WO 95/05354 describes the hydroformylation of ethylenically unsaturated compounds by reaction with carbon monoxide and hydrogen in the presence of a catalyst system comprising a Group VIII metal cation, viz. cationic palladium, and a bidentate ligand, viz. a diphosphine. In the examples several bidentate diphosphines are used.
However, currently known methods for producing primary alcohols suffer from the disadvantage that they are restricted to feedstock which is relatively expensive, notably ethylene, which is produced via the thermal cracking of paraffins. In addition, current methods require several steps, and several catalyst types. Considering the production of primary alcohols by hydroformylation, first it is necessary to prepare ethylene via the thermal cracking of paraffins. Thereafter it is necessary to prepare an olefin feed, for example by ethylene oligomerization in the presence of an oligomerization catalyst, and finally, in a further separate step, the olefins are converted to alcohols by hydroformylation in the presence of a hydroformylation catalyst.
From the viewpoint of reducing cost, it would clearly be desirable to develop a process which can make use of relatively inexpensive feedstock, eg. secondary or tertiary alcohols and ketones derived from the oxidation of paraffin. It would also be desirable to provide a process whereby primary alcohols are produced using a smaller number of steps than currently known processes.
It has now surprisingly been found that by reacting secondary alcohols, primary alcohols or ketones, or mixtures of one or more of these, with carbon monoxide and hydrogen in the presence of excess acid and a Group VIII metal catalyst having a bidentate ligand, a “single-pot” process for producing primary alcohols is achieved.
The process of the present invention also has the advantage that it is possible to simultaneously or separately prepare olefins in addition to primary alcohols. Higher olefins are useful in drilling fluid applications as well as a variety of other applications.
A further advantage of the present invention is that there is a high selectivity towards linear primary alcohols, which are known to be more biodegradable than branched primary alcohols and therefore are particularly useful intermediates for surfactants which are used in laundry detergent applications.